The behaviour of a certain gas is described by the van der Waals equation 2 P = 0.02T V-0.007 V2 where P is pressure, V is volume and T is temperature. At T = 313 K and V = 2 l, find the rate of change of P if the temperature increases at the rate of 0.2 Ks while the volume decreases at the rate of 0.3 ls-.